The present invention relates to a bearing unit which is included in the clutch mechanism of a motor vehicle having a manual transmission and is for releasing a clutch. The present invention more particularly related to a bearing unit which is included in the pull-type clutch mechanism of a motor vehicle having a manual transmission and pulls the central portion of a diaphragm spring to release a clutch at the time of manipulating the transmission to change the speed of the vehicle.
A clutch mechanism provided at the manual transmission of a motor vehicle includes a flywheel which is rotated together with the crankshaft of the engine of the vehicle; a clutch disk facing the flywheel; a pressure plate for pushing the disk toward the flywheel; a diaphragm spring for pushing the pressure plate toward the clutch disk; and a bearing unit which can be moved along a motive power shaft to change the angle of the inclination of the diaphragm spring to engage or disengage the flywheel and the clutch disk with or from each other. Many of conventional such clutch mechanisms are of the push type in which the central portion of the diaphragm spring is pushed to release a clutch in such a manner that the flywheel and the clutch disk are separated from each other to keep the torque of the crankshaft from being transmitted to the transmission through the motive power shaft.
When the clutch of the push-type clutch mechanism is to be engaged to transmit the torque of the crankshaft to the manual transmission through the motive power shaft, the clutch disk 3 is pushed onto the flywheel with the pressure plate 2 by the elastic force of the diaphragm spring 1 as shown in FIG. 10. When the clutch is to be released to keep the torque of the crankshaft from being transmitted to the manual transmission through the motive power shaft at the time of manipulating the transmission to change the speed of the vehicle, the central portion of the diaphragm spring 1 is pushed down (as to FIG. 10) toward the flywheel by the bearing unit so that the angle of the inclination- of the spring is changed, as shown in FIG. 11, to cause the pressure plate 2 to stop pushing the clutch disk 3.
On the other hand, a pull-type clutch mechanism includes a diaphragm spring 1 of larger leverage and a less deformed clutch cover 4 than the push-type clutch mechanism, and transmits higher motive power than the push-type one. The pull-type clutch mechanism has recently been used for a heavy vehicle or the like in the main. When the clutch of the pull-type clutch mechanism is to be engaged to transmit the torque of the engine of a motor vehicle through a motive power shaft, a clutch disk 3 is pushed onto a flywheel with a pressure plate 2 by the elastic force of the diaphragm spring 1 similarly to the push-type clutch mechanism, as shown in FIG. 12. When the clutch is to be released to keep the torque of the engine from being transmitted to the manual transmission through the shaft at the time of manipulating the transmission to change the speed of the vehicle, the central portion of the diaphragm spring 1 is pushed up (as to FIG. 12) away from the flywheel by a clutch release bearing unit so that the angle of the inclination of the diaphragm spring is changed, as shown in FIG. 13, to cause the pressure plate 2 to stop pushing the clutch disk 3.
FIG. 14 shows the constitution of the conventional bearing unit 5 of the pull-type clutch mechanism. The bearing unit 5 comprises a sleeve 6 movable along the guide shaft or front cover of the clutch mechanism; a support plate 7 which is an annular metal plate secured to the outer circumferential surface of the sleeve; a ring 9 secured to the peripheral portion of the support plate and having a holding portion 8 shaped as a short cylinder; a clutch release bearing 10 fitted in the holding portion; and an operating cylinder 11 rotatably supported by the bearing in order to pull the central portion of the diaphragm spring 1. The peripheral portion 12 of the support plate 7 is bent back so as to hold the bent outer portions 13 of the ring 19 at one end thereof in such a manner that the plate and the ring are coupled to each other. The ring 9 has engagement portions 14 located opposite each other in the diametral direction of the ring. The tip portions of the arms of the clutch releasing fork of the clutch mechanism are engaged with the engagement portions 104 of the ring 9 along with the swing of the fork so as to pull the clutch release bearing 10 rightward as to FIG. 14. The inner circumferential edge portion of the pull plate of the clutch mechanism is fitted in the recess 15 of the outer circumferential surface of the end portion of the operating cylinder 11 and the pull plate faces the inner circumferential edge portion of the diaphragm spring 1 so that the plate pulls the central portion of the spring as the operating cylinder is moved.
Since the bent-back peripheral portion 12 of the support plate 7 of the conventional bearing-g unit 5 is engaged with the bent outer portions 13 of the ring 9 of the unit in order to couple the support plate and the ring to each other, the joint of both the plate and the ring projects by a length h outward from the outer circumferential surface of the body of the ring, as shown in FIG. 14. For that reason, many components of the clutch mechanism need to be located at relatively large distances from the bearing unit 5 in order to prevent the joint from interfering with the components. As a result, the degree of freedom of the design of the clutch mechanism is lowered. Since the bent-back peripheral portion 12 of the metal plate 7 is bent twice, high residual stress is caused in the portion to make it likely to undergo a crack in the long-period use of the portion.
To solve these problems, arts were developed as disclosed in Japan Utility Model Application (OPI) No. 2-84021 (the term "OPI" as used herein means an "unexamined published application"). In one of the arts, the outer end portion of the ring 9 of a bearing unit is provided with a thin part 16, the outer circumferential edge portion of the support plate 7 of the unit is fitted on the inner surface of the thin part, and the projecting portion of the thin part, which projects from the support plate outward along the axis of the ring, is bent inward in the radial direction of the ring to couple the plate and the ring to each other, as shown in FIGS. 15 and 16. In the other of the arts, the outer circumferential portion of the support plate 7 of a bearing unit is provided with a cylindrical part 17, the part is butted at the end thereof to the inner surface of one inwardly bent end portion 18 of the ring 9 of the unit, and the other end portion 19 of the ring, which projects from the cylindrical part outward along the axis of the ring, is also bent inward in the radial direction thereof to pinch the cylindrical part between both the inwardly bent end portions to couple the support plate and the ring to each other, as shown in FIG. 17. However, since the support plate 7 and the ring 9 are coupled to each other by bending the ring in each of the arts, the ring needs to be made of a bendable relatively soft material not subjected to quenching or the like and is therefore likely not to be high enough in strength. Since a strong force larger than the elastic force of a diaphragm spring is applied to the ring 9 by a releasing force to release a clutch, the ring needs to be high enough in flexural strength. If the ring 9 is made of the relatively-soft material, it is difficult to render the ring high enough in flexural strength. For that reason, it is hard to use the ring 9 of such a soft material for a heavy vehicle having a diaphragm spring of strong elastic force. Although it is conceivable to subject the to-be-bent portion of the ring 9 to a carbon blocking treatment and thereafter quench the other portion thereof to make it possible to render the ring high enough in strength and bend the former portion, the processing of the ring is troublesome and the cost of manufacturing thereof is high.